An example of a rear-projecting device is within the technical area of traffic signs.
The area of traffic signs represents a technical area within which many attempts to modernize the traditional signing have more or less failed due to various circumstances.
Hence, the traditional mechanically based traffic sign having one static painted signaling surface represents the dominating traffic sign of today.
Nevertheless, several attempts of breaking the dominance of the above-mentioned technique have been made due to the fact that an effective variable traffic sign would provide immense improvements in regard to traffic control.
One of the frequently used types of variable traffic signs comprises small rotatable mechanical elements having e.g. three different surfaces, each surface being dedicated to a certain sign. Thus, a sign may change between three different sign states by means of synchronous rotating of the sign element. Such signs represent a well-proven technique providing a visual quality comparable with standard traditional traffic signs. However, the sign is quite restricted with respect to other variations.
Another type of a variable traffic sign is represented by signs having a plurality of light sources spread all over a signaling surface. The light sources may e.g. comprise small lamps or light emitting diodes (LEDs). Such signs represent a technique having a very high degree of variation as the number of possible variations is only restricted by the resolution of the sign. However, due to the very discrete, low-dense positioning of light sources, this type of sign has found very little use within the area of traffic signs with the exception of traffic signs having quite few “high power” light sources, and consequently a few possible variations due to low resolution problems. Moreover, a sign of this type becomes extremely expensive, when growing in dimensions.
Another serious problem related to the prior art projecting devices is that a very large amount of illumination power is required over a homogenous projecting area.
Thus, a rear projection device having a large degree of variation combined with large dimensions is desired.